Also thanks to virtualization being originally invented in mainframes, and the OS design done by IBM (and Unisys as well), they get to run the old workloads on

Also thanks to virtualization being originally invented in mainframes, and the OS design done by IBM (and Unisys as well), they get to run the old workloads on modern hardware, and also support various UNIX flavours. You can even run most cool Python, Go, Java, Rust, PHP among others, on systems like z/OS.